Next Step in Outbreak Investigation
The next step is to conduct a case-control study to systematically identify specific food items or exposures associated with illness (Option B). 1
Rationale for Case-Control Study
The outbreak investigation follows a structured sequence of phases, and you have already completed the initial phase by establishing that an outbreak exists (15 of 50 staff ill with similar symptoms and common restaurant exposure). 1 The current phase requires conducting a formal case-control study to:
- Quantify the strength of association between suspected exposures and illness using odds ratios, which will identify the specific contaminated food item rather than making assumptions about all restaurant foods being equally risky 1
- Guide targeted control measures based on identified risk factors rather than implementing broad, resource-intensive interventions without epidemiologic direction 1
- Compare cases (ill staff) with controls (well staff who also ate at the restaurant) through structured interviews about specific food items consumed 1
Why Other Options Are Premature
Isolation (Option A)
- Isolation of affected individuals is not the immediate priority in a foodborne outbreak investigation where the source remains unidentified 2
- This would be appropriate later for specific pathogens with person-to-person transmission concerns (e.g., norovirus), but only after identifying the source 2
Quarantine Restaurant Staff (Option C)
- Quarantining restaurant staff without epidemiologic evidence identifying the specific food vehicle wastes time and resources 1
- While food handlers may need exclusion if found to be infected, this determination comes after the case-control study identifies the implicated food and subsequent environmental investigation 2, 1
Environmental Investigation (Option D)
- Delaying the case-control study to pursue environmental investigations first wastes time and resources without epidemiologic direction 1
- The environmental and laboratory investigation (including collecting food samples and screening food handlers) is the subsequent phase that follows the case-control study 1
- Without knowing which specific food item is implicated, you cannot efficiently direct environmental sampling efforts 3
Practical Implementation
The case-control study should:
- Define cases using clinical criteria (acute gastroenteritis with specific symptom onset timing) 2
- Identify controls from the same population (hospital staff who ate at the restaurant but remained well) 2
- Conduct structured interviews about all specific food items consumed at the restaurant 1, 3
- Calculate odds ratios for each food exposure to identify the vehicle of infection (as demonstrated in similar outbreaks where specific items like potato salad showed OR of 84.0) 1
Critical Pitfall to Avoid
Do not assume all restaurant exposures are equal—the case-control study will likely identify one or two specific high-risk food items rather than general restaurant exposure. 1 Historical outbreak investigations have shown that specific items (roast rabbit, turkey salad sandwiches, tuna salad, curly-fried potatoes) were implicated rather than all foods from the establishment. 3, 4, 5